In Japan, a PS Vita version is already available. The new versions will cost 3,200 yen, but launch at a discounted price of 2,550 yen until January 8.

The new versions are ported from the PS Vita, iOS, and Android versions of Romancing SaGa 2. Graphics have been readjusted for each platform. The PlayStation 4 version supports cross-save with the PS Vita version, and the Xbox One version does the same with the Windows 10 version.

Here is an overview of the game, via Square Enix:

Originally released in 1993, the landmark title in the SaGa series has players leading the Varennes Empire in battle against the Seven Heroes. A free scenario system—a hallmark of the SaGa series—enables the player to take command of a variety of protagonists along the line of imperial succession and experience the history of a nation as it grows and changes.
Enhanced features include:

Updated graphics and audio

New character classes provide added depth and tactical possibilities to gameplay

New dungeon provides greater challenges

“New Game+” feature carries over useful character attributes and items into a new game, enabling players to obtain missed items, or save previously sacrificed lands and companions.

In related news, Square Enix said that the March-announced remaster of Romancing SaGa 3 is currently 60 to 70 percent complete.

For further reading, PlayStation Blog Europe has an interview with SaGa series director Akitoshi Kawazu.